Titanium base alloys with aluminum, manganese, and chromium



TITANIUM BASE ALLQYS WlTH ALUMINUM, MANGANESaE, AND CHROMIUM Paul S. Methe, Cohes, N. Y., assignor to Allegheny Ludlum Steel Corporation, Brackenrirlge, Pa, a corpora tion of Pennsylvania No Drawing. Application November 17, 1953, Serial No. 392,749

3 Claims. (Cl. 75-177) This. invention relates to titanium-base alloys, and in particular to titanium-base alloys containing aluminum and beta stabilizers.

Heretofore titanium-base binary alloys containing aluminum in excess of 6% have been prepared in limited quantity since considerable difiiculty has been experienced =2 Since aluminum has the effect of raising the alpha to alpha plus beta transus temperature, the alloy system of aluminum and titanium would appear to be quite desirable from the standpoint of elevated temperature service, especially in the range from 800 F. to 1200" F. However, while the binary alloys of the titanium-aluminum system have the requisite high temperature stability, they do not possess sufiicient ductility when the aluminum content is greater than 6% to permit them to be cornrnercially fabricated.

An object of this invention is to provide a titaniumbase alloy having a relatively high aluminum content and having small but critical amounts of manganese and chromium.

Another object of this invention is to provide a titanium-base alloy having a substantial amount of aluminum and small but critical percentages of manganese and chromium, the alloy being characterized by retaining substantial ductility after being heated to a temperature of 1700 F.

A further object of this invention is to provide a titanium-base alloy having aluminum, manganese and chromium contained therein, the alloy having a structure consisting of the beta phase in a matrix of the alpha phase with the alpha phase being predominant, said alloy having good ductility after having been forged at a temperature in the range between 1700 F. and 2000 F.

Another object of this invention is to provide a titanium-base alloy having aluminum and small but critical amounts of manganese and chromium contained therein, the alloy being characterized by having excellent elevated temperature creep-rupture properties.

These and other objects of this invention will become apparent to those skilled in the art when read in conjunction with the following description.

in accordance with this invention the titanium alloys of this invention are composed of aluminum in the range from 6.5% to 10%, and small but critical amounts of two beta stabilizers consisting of manganese and chromium. Each of the beta stabilizers present in the alloy is preferably maintained Within the range between 0.75% and 1.25%. The balance of these alloys is composed of titanium with incidental impurities, such as not more than What little ductility these ".1

atent Table I General Optimum K4025 Element Range Range In all cases the balance of the alloys of Table I is titanium with incidental impurities.

The alloys of this invention can be prepared in any well-known manner, for example, by tungsten are melting, or the consumable arc melting processes. In order to introduce a specific amount of the alloying elements into the titanium base and thereby obtain the titaniumbase alloy of the desired chemical composition, the alloying additions may be made in the form of either virgin metals, aluminum master alloy, or a combination of both. However, the manner of addition will depend upon the type of melting employed, namely, tungsten are melting, or consumable arc melting. When the tungsten arc melting is employed, the alloying elements are blended with the titanium sponge, and the blended mixture is introduced into the molten pool of metal which is formed by the passage of electrical energy between the tungsten electrode and the metal charge, thus creating an arc and thereby melting the metal. On the other hand, if a consumable electrode is employed in arc melting the alloys, the alloying components are preferably added as part of the consumable electrode per se.

Since aluminum has the efiect of raising the alpha to alpha plus beta transus temperature and the alpha plus beta to beta transus temperature in a titanium-base alloy, the temperature range under which the alpha phase exists is much broader where the aluminum is a component of the alloy. However, since the alpha phase has a closepacked hexagonal crystallographic lattice configuration, it exhibits low ductility in comparison to the body-centered cubic structure of the beta phase. To overcome the low ductility of the close-packed hexagonal lattice structure of the alpha phase, small but critical amounts of beta stabilizers, which form a body-centered cubic crystallographic lattice of the beta phase and which exhibits considerable ductility, are added to the titaniumaluminum-base alloy to increase the over-all ductility of these alloys. At the same time, however, the beta stabilizers do not prove detrimental to the creep-rupture properties nor the alpha stability at elevated temperatures. In so doing, the toughness exhibited by the alpha will remain, but the alloys will have sufiicient ductility to be fabricated economically.

It has been found also that small but critical percentages I of each beta stabilizer has a more desired effect than larger percentages of either one. For example, it has been found that the effect of about 1% manganese and about 1% chromium has a greater beneficial effect for the purposes of these alloys than about 2% of either manganese or chromium. While the reason for accomplishing this cfect is not clear, it is believed that each element has a multiplying eifect on the over-all alloy rather than an additive effect.

In order to fabricate the alloys of this invention, such as the alloy identified as K-1025 in Table I, it may be forged from a temperature in the range between 1750 and 2000 F. The step of forging is performed on the cast ingot to break up the as-cast structure. After forging, the ingot may be rolled in a conventional manner, as will hereinafter be described. The forged alloys are preferably preheated to a temperature of 1400 P. where they are held for a period of about two (2) hours,

chanical properties of the alloy at elevated temperatures, especially creep-rupture strengths, is the usual governing criteria when selecting the proper metal to be utilized. Reference may be had to the results recorded in Table III for the outstanding creep-rupture properties of alloy D or until such time as the ingot has soaked to a uniform K].O25 as measured at the elevated temperatures inditemperature of 1400 F. Of course, as is well-known, the cated. time to soak to a uniform temperature will vary with Table III the bulk of the metal employed. After the ingot has attained a uniform temperature of 1400 F., the tempera- 10 second ture is raised to l650 P. where it is held for a period Stress Test Failure ary w of about one half hour to develop a substantially uni- Heat Treatment l 5:5; 5;; 523 form temperature, and thereafter the forged alloy is hot hr.) rolled to the desired size in any conventional rolling mill. /h V As an example of the heating and rolling procedure 1 1 85,000 2 1111 I111 .00045 employed in the fabrication of the alloys of this inven- D0 60000 800 547% ml ml 00045 tion, alloy K-l025, hereinbefore referred to, was proc- ,mscontmuedfiid notmpwre essed in the following manner. This alloy, an elevenpound ingot, was forged at a temperature of 1850" F. to Fmm the results recordeq f In, t m be a X billet, after which it was allowed to cool 20 served that the alloys of this lnventlon exhlblt excellent in air. The billet was then preheated to 1450 F. for two G w- 12 Props,16s at elevated temperatures- There (2) hours after which time it was heated to 1650 F '18 very llttle elongatlon and the percent creep per hour held at this temperature for about one h lf hour, and in the test lndlcates excellent creep-rupture strength. It thereafter hot rolled to a 4-inch round bar. Reference is noteworthy to Point out that the alloys of this invention may be had to the alloys 14-1025 and K803 in Table II 25 did not fail during the m e than 500 hours t e for the purpose f comparing the room temperature vated test temperatures lndlcated. It ls also slgnlfieant il ti All K4025 was refer ed to i T bl to observe that while these alloys have been heated to a I, while alloy K-803 is a binary titanium-aluminum alloy temperature of 1700 F. and thereafter subjected to elecontaining 8% aluminum. vated temperature under stress for a prolonged period Table II Alloy Heat Treatment (air cooled) g g g Re As rolled 192,500 190,500 16.0 31.4 44.0

1 hr. 1,500 151,000 22.0 40.5 40.0 K4025 hrs. l,200

2hrs. l,450 150, 000 21.0 44.0 38.8

24 hrs. 1, 155,500 22.0 45.2 38.6

As forged 134,000 4.0 7.1 32.3

1 hr. 1,70 128, 500 4. 0 13. 9 32.0 K-s03 1hr. @1,40 133, 700 3.0 4.1 29.3

2hrs. 1,200 F. 143,000 5.0 6.3 32.0

24 hrs. 1,200 44,300 4.7 34.0

It is quite evident from the inspection of Table II that of time, the alloys of this invention possess excellent the addition of the two beta stabilizers within the limits creep-rupture strength. given produces an alloy of superior characteristics. For I claim: example, the tensile strength of alloy K-1025 is far supe- 1. An alloy consisting of, from about 6.5 to about rior to that of binary alloy K-803. The elongation and 10% aluminum, from about 0.75% to 1.25% manganese, especially the reduction of area test proves the superiority from about 0.75% to 1.25% chromium, and the balance of alloy K-l025 over and above K-803. This is most ap- 5U titanium with incidental impurities.

parent when comparing the two alloys having the same heat treatment, namely, one hour at 1700 F. and 24 hours at 1200 F.

However, the above mentioned properties of these alloys are room temperature properties. It is well-known that the mechanical properties of an alloy differ at elevated temperatures from the mechanical properties measured at room temperature. In any true engineering application involving use at elevated temperatures, the me/ 2. All alloy consisting of, from about 6.5% to about 8% aluminum, from about 1% to about 1.15% manganese, from about 1% to about 1.15% chromium, and the balance titanium with incidental impurities.

3. An alloy consisting of, about 7% aluminum, about 1% manganese, about 1.15% chromium, and the balance titanium with incidental impurities.

No references cited. 

1. AN ALLOY CONSISTING OF, FROM ABOUT 6.5% TO ABOUT 10% ALUMINUM, FROM ABOUT 0.75% TO 1.25% MAGANESE, FROM ABOUT 0.75% TO 1.25% CHROMIUM, AND THE BALANCE TITANIUM WITH INCIDENTAL IMPURITIES. 